The invention relates to a key switch unit made of synthetic material comprising a key switch housing and at least one key top with a corresponding spring section.
Such key switch units are used, for example, as control elements in front panels of household appliances such as wash machines or dishwashers and the like. The key switch unit is typically placed between a panel and a circuit board with electronic components in such a manner that the key top is located in an opening of the panel whereby down-ward force exerted on the key top is transferred via the spring section onto a switch, which is mounted on the circuit board. The spring section has the function to limit the force transferred to the switch whereby the small switch and the circuit board are not damaged even during forceful manual actuation of the key top.
Since the key top and the spring section are positioned on top of one another and since they mostly consist of different materials, they are currently manufactured as two separate components. Typically, several keys are positioned next to one another within the key switch unit. The spring sections, which are positioned parallel to one another, are connected to a so-called spring rack, whereas the key tops and the key switch housing are separate components, which have to be attached manually to the spring rack.
It is the object of the invention to reduce assembly steps during manufacturing of the key switch unit.
This object is achieved according to the invention in that the key switch housing, the key top and the spring section are made in one piece wherein the key top is connected with the spring section by a strip hinge and whereby the key top can be folded back against the spring section.
The entire key switch unit may thereby be injection-molded in one piece with synthetic material, whereby the workpiece is designed in such a manner that the spring section and the key top are connected with a strip hinge in a straight position, so that both parts are essentially positioned at one plane whereby they may be easily deformed. During assembly, the key top is folded back against the spring section so that the spring section can be actuated by the key top. The complete key switch unit may then be mounted in this condition to the panel as a single component. Thereby no additional work steps are necessary for positioning and assembly of key tops and spring sections.
By using a multi-component, injection-molding process it is possible to manufacture the key tops and spring sections out of different materials even in the one-piece construction method so that the key top has a great mechanical stability. The key top may consist of a relatively hard and easy-to-clean substance whereas a more resilient material may be used for the spring section.
The key top may also be constructed in two layers. Thereby it is made possible to give the key top a two-color marking wherein a different-colored material is used in the lower layer of the key top and whereby an opening is created in the upper layer, which allows viewing of the lower layer or whereby the opening is filled with the material used in the lower layer.
Oftentimes the key tops have an indicator light, which is mounted on the circuit board and whereby its light is transmitted through a window or an optical light conductor to the front of the panel. According to further development of the invention, this window or the optical light conductor may also be manufactured in one piece together with the remaining elements of the key switch unit. A second or third material component consisting of a transparent or translucent synthetic material is used to make the window or the optical light conductor, respectively.
In some versions there is also a high-tension component located on the circuit board in addition to the low-voltage component, which includes relatively heavy components such as transformers and the like. In this case it is necessary for stability purposes to mount the circuit board in a circuit board housing made of synthetic material. In a special embodiment of the invention, this circuit board housing may also be manufactured in one piece together with the remaining elements of the key switch unit whereby this circuit board housing may be connected to the key switch housing with an additional strip hinge so that it may be folded back.